Heat Resistant Laminate and Method for Manufacturing Such Laminate

ABSTRACT

According to the invention, there is provided a more heat-resistant laminate comprising a metal foil, a fabric, and bonding means between the metal foil and the fabric, wherein the bonding means are a flouropolymer foil functioning as an adhesive film for bonding the fabric and the metal foil together. Hereby, an impermeable laminate is provided which is flexible and can withstand higher temperatures without delaminating. A laminate according to the invention can be mounted directly against hot components with temperatures up to 550° C. when the fabric is a woven glass fabric and as high as 1100° C. if the fabric is ceramic. The bonding means are stabile in temperatures up to 290° C. and provides a stabile and durable bonding also during temperature exposure of the laminate of 310° C. for an extended period of time.

The present invention relates to a laminate in particular for protectionagainst heated, aggressive media in an expansion joint and a method ofmanufacturing such laminate.

In the field of covers for protection against aggressive medias, such asexpansion joints in channel constructions in flue gas plants, the flowchannels are exposed to gas heated to temperatures above 260° C. Forthis purpose, it is known to use several layers of laminated foils orfabrics for designing a gas and fluid-tight connection joint in order toretain the media, such as e.g. flue gas with a high temperature andother aggressive medias inside the channels.

The disadvantage by these known cover types is that the most suitablematerial available from a temperature perspective and which isrelatively fluid-tight and flexible is a flouropolymer foil with anupper temperature limit of 270° C. and it is therefore necessary toinsulate this foil from the parts of the construction where thetemperature is above this temperature.

Typically, the temperature in sections of such channel constructions mayreach 270° C. to 700° C. or more and it is therefore necessary toprovide one or more glass fabrics, modified glass fabrics or the like ina sandwich construction in several layers underneath thefluid-tightening layer until a maximum temperature limit below 270° C.is achieved. However, these layers of woven fabrics are permeable and donot prevent the leakage of unwanted medias escaping from the flowchannels and into the surroundings.

It is known to use a laminate material for the gas-tight layer, which isa thin steel foil with a silicone adhesive intermediate layer so that aglass fabric is fixed to the steel foil. Although this laminate materialis impermeable, the maximum temperature exposure that the laminate canwithstand is 250° C. By a higher temperature exposure a very rapiddeterioration of the laminate will occur causing a destruction of thelaminate.

On this background, it is an object by the present invention to providea laminate which is impermeable and that can withstand highertemperatures.

According to the invention, this object is achieved by a moreheat-resistant laminate comprising a metal foil, a fabric, and bondingmeans between the metal foil and the fabric, wherein the bonding meansare a flouropolymer foil functioning as an adhesive film for bonding thefabric and the metal foil together.

Hereby, an impermeable laminate is provided which is flexible and canwithstand higher temperatures without delaminating.

A laminate according to the invention can be mounted directly againsthot components with temperatures up to 550° C. when the fabric is awoven glass fabric and as high as 1100° C. if the fabric is ceramic andremain although as single layer.

The bonding means are stabile in temperatures up to 290° C. and providesa stabile and durable bonding also during temperature exposure of thelaminate of 310° C. for an extended period of time. To obtain thisstability, a surface treatment may be necessary, eg. in form ofacid-washing.

By the invention, it is realised that the laminate is suitable for usein different applications where the temperature exceeds 300° C. wherethe bonding means only function as positioning and holding the metalfoil in place until the laminate is mounted and taken into operation. Bythen, the metal foil will serve as an impermeable barrier irrespectiveof whether the glass fabric is detached from the metal foil or not.

The metal foil is preferably a stainless steel foil. However, it isrealised that other types of thin metal foil may be used, such asaluminium, brass, copper or metal alloys. The metal foil is between 0.01to 1 mm in thickness, preferably 0.0254 mm (0.01 inch) in thickness.

The woven fabric preferably has a grammar weight between 50 to 3000g/m². The fabric may be a woven glass fabric, preferably having agrammar weight of approx. 700 g/m². Alternatively, the fabric may be asilicate fabric or a ceramic fabric, preferably having a grammar weightbetween 600 to 700 g/m².

The flouropolymer foil is preferably between 0.01 to 1 mm in thickness.The material of the flouropolymer foil could be PFA (perfluoro alkoxy).Other suitable materials for the flouropolymer foil are MFA(perflourmethylvinylether), FEP (Fluorinated ethylene propylene), TFE(tetra flour ethylene), ETFE (ethylene tetra flour ethylene), ECTFE(ethylene chloride triflour ethylene) TFM (modified poly tetra flourethylene) or virgin PTFE (poly tetra flour ethylene).

In the preferred embodiment, the metal foil is provided with an enchasedtexture whereby the foil is provided with an array of miniatureembossing on at least a part of the foil. Hereby, the durability of thelaminate is significantly improved. It is also possible to usepre-embossed foils, which will also enlarge the durability of theproduct.

When the laminate is used in an expansion joint, the laminate isfrequently flexed, and after only a few bends, notches or indents willappear in the foil. At these indents the foil is stressed as the foilwill continue to bend at these indents and the foil will eventuallycrack due to metal fatigue due to the stress. However, by providing thefoil with an enchased foil texture, the foil is provided with an arrayof small soft dimples, stress concentrations are avoided and the bendingduring use will take place at different places in the foil and not atthe same spot every time. This reduces the wear of the metal foil andthus improves the durability of the laminate.

In another aspect, the invention concerns a method of manufacturing alaminate including the steps of providing a first layer of metal foil;providing a second layer of thermoplastic flouropolymer; providing athird layer of fabric; assembling the first, second and third layers,pressing the assembly of layers while heating the assembly in a heatingzone to a temperature above the melting point of the intermediate secondlayer for a predetermined amount of time for laminating the first andthird webs together; and cooling the laminate while pressing thelaminate in a cooling zone.

In the following, the invention is described in detail with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic cross section view of the laminate according tothe invention before lamination;

FIG. 2 is the same after lamination;

FIG. 3 is a schematic view of a first embodiment of the laminationmanufacturing process; and

FIG. 4 is a second embodiment of the lamination manufacturing process.

In FIGS. 1 and 2 the laminate according to the invention is shown beforeand after lamination. A thin metal foil, which is embossed during theprocess or pre-embossed, preferably a steel foil 1 is provided with athin flouropolymer foil, preferably a PFA foil 2 and a glass fabric 3.The PFA foil 2 acts as bonding means between the steel foil 1 and theglass fabric 3. The three layers 1, 2, 3 are pressed against each otherand simultaneously heated to an elevated temperature. Hereby, the PFAfoil 2 melts and becomes liquidized and binds the metal foil 1 and thefabric 3 together. The laminate is subsequently cooled in a coolingzone. During the cooling, the layers in the laminate are kept pressedagainst each other.

The steel foil 1 and the PFA foil 2 are preferably 0.0254 mm (1 mil) inthickness. The thin steel foil 1, embossed during the process orpre-embossed, is provided with an enchased texture to ensure a bothflexible and durable foil—and laminate respectively. Preferably, theenchased texture is provided the foil when it is pressed against thewoven glass fabric (with the PFA foil in between). Hereby, theundulations on the foil match the surface contour of the fabric. Thisresults in a strong bonding as well as a flexible laminate.

In FIGS. 3 and 4, two embodiments of the manufacturing process areschematically shown.

Adjacent a pressing apparatus, a three supply rolls are provided. Fromthese supply rolls a web of steel foil 1, embossed during the process orpre-embossed, a thermoplastic PFA foil 2 and a glass fabric 3 areprovided. The three layers are forwarded into a pressing section andassembled. The pressing section includes a heating zone 5 and a coolingzone 6. The heating zone 5 includes in a first embodiment, shown in FIG.3, a set of pressing members 51, e.g. pressing members or jaws, and asupport web 52 on each side of the assembled laminate web 4. The coolingzone 6 also includes a set of pressing members 61 with associatedsupport webs 62 arranged on each side of the assembled material web 4.

The support webs 52, 62 protect the material webs 1, 3 from both sidesin the heating and cooling zones 5, 6. The geometric surface texture ofthe support webs 52, 62 are advantageously adapted so that the steelfoil 1 is provided with an array of soft dimples so that the foil 1during the pressing action is provided with an enchased texture, whichensures a longer durability by frequent bending/flexing of the laminate.

The assembled laminate web 4 is forwarded through the two pressingmembers 51 in the heating zone and is held there under pressure for aperiod of 10 to 300 seconds, which makes the thermoplastic flouropolymerfoil 2 liquidized due to the simultaneous heating to a temperature of327 to 400° C. Then the assembled laminate web 4 is pulled forward bythe advancing means 7 and the heated material web 4 is retained underpressure between cooling members 61 and is cooled normally to ambienttemperature, but depending on the actual requirements to the resultinglaminate, a cooling to a temperature between 0° C. to 250° C. isperformed, where an ambient temperature (such as 20 to 30° C.) ispreferred. The laminate web 4 may be intermittently forwarded throughthe pressing section, i.e. the heating and cooling zones 5, 6. Thelaminate is finally wound up on a roll 41.

As shown in FIG. 4, the pressing members in the heating and coolingzones 5, 6 may alternatively include rollers 53, 63. In this embodiment,the laminate web 4 may be continuously forwarded through a set of heatedpressure rolls 53 and subsequently a set of cooling pressure rolls 63.In order to ensure that the flouropolymer remains melted between the twosets of pressure rollers 53, 63, heating means 54 are provided therebetween, so that the required bonding strength between the steel foil 1and the fabric 3 is achieved.

The steel foil 1 is an ultra thin metal foil with a thickness between0.01 to more than 1 mm, preferably 0.0254 mm (1 mil) and embossed duringthe pressing process or pre-embossed. The flouropolymer foil may bebetween 0.01 mm and 1 mm in thickness and would preferably be of a PFA(perfluoroalkoxy) material. Other suitable materials for theflouropolymer foil are MFA (perflourmethylvinylether), FEP (Fluorinatedethylene propylene), TFE (tetra flour ethylene), ETFE (ethylene tetraflour ethylene), ECTFE (ethylene chloride triflour ethylene) TFM(modified poly tetra flour ethylene) or virgin PTFE (poly tetra flourethylene).

The woven fabric preferably has a grammar weight between 50 to 3000g/m². The fabric may be a woven glass fabric, preferably having agrammar weight of approx. 600 to 700 g/m². Alternatively, the fabric maybe a silicate fabric or a ceramic fabric, preferably having a grammarweight of 600 g/m².

Other types of ultra thin metal foils embossed during the process or preembossed, could be aluminium, brass, copper or other metal alloys.However, when using PFA as bonding means one must observe that themelting point of the metal is above 400° C. and the maximum allowedtemperature of the laminate may be limited by the type of metal used inthe laminate.

If other metals are chosen having a melting point, which is lower, a FEPfoil could be used as bonding means between the fabric and the metalfoil. Hereby, a lower working temperature of about 210° C. is achieved.

By the term enchased texture of the metal foil, is meant any kind ofrepetitive deformation structure of the otherwise plane surfacestructure of the foil.

According to the invention, the metal foil is enchased during thepressing in the lamination process. Hereby, an extra process step isavoided and as a consequence a reduction of production costs may beachieved.

According to the preferred manufacturing process, the metal foil isprovided with an enchased surface during the pressing in the heating andcooling zones, where the pressure is between 5 kg/cm² and 1000 kg/cm²depending on the metal foil which is used in the laminate.

By the invention, it is realised that the undulations or dimples in theenchased texture must be soft rounded shapes, since sharp edges will bestress built-up points in the foil and result in a reduction of thedurability of the foil/laminate. A metal fatigue is quickly achieved ifsharp edges occur because the bending points or bending lines willre-occur at the same line/point every time. By the soft undulations thebending will occur over a larger area and it is found that thedurability may be improved by 20-40%.

1. A heat-resistant laminate comprising a metal foil a fabric, andbonding means between the metal foil and the fabric, wherein the bondingmeans are a flouropolymer foil for bonding the fabric and the metal foiltogether, characterised in that the metal foil is provided with anembossed texture whereby the foil is provided with an array of miniatureembossing on at least a part of the foil.
 2. A laminate according toclaim 1, wherein the metal foil is a stainless steel foil.
 3. A laminateaccording to claim 1 or 2, wherein the metal foil is between 0.01 to 1mm in thickness, preferably 0.0254 mm (0.01 inch) in thickness.
 4. Alaminate according to any of claims 1 to 3, wherein the metal foil isprovided with an embossed texture as the foil is provided with an arrayof miniature embossing on at least a part of the foil during process andalso pre-embossed.
 5. A laminate according to any of claims 1 to 4,wherein the woven fabric has a grammar weight between 50 to 3000 g/m².6. A laminate according to claim 5, wherein the fabric is a woven glassfabric, preferably having a grammar weight of approx. 700 g/m².
 7. Alaminate according to any of claims 1 to 4, wherein the fabric is asilicate fabric or a ceramic fabric, preferably having a grammar weightof 600 g/m².
 8. A laminate according to any of the preceding claims,wherein the material of the flouropolymer foil is PFA (perfluoroalkoxy).
 9. A laminate according to any of claims 1 to 7, wherein thematerial of the flouropolymer foil is MFA (perflourmethylvinyleiher),FEP (Fluorinated ethylene propylene), TFE (tetra flour ethylene), ETFE(ethylene tetra flour ethylene), ECTFE (ethylene chloride triflourethylene) TFM (modified poly tetra flour ethylene) or virgin PTFE (polytetra flour ethylene).
 10. A laminate according to any of the precedingclaims, wherein the flouropolymer foil is within the range of 0.01 to 1mm in thickness.
 11. A method of manufacturing a laminate including thesteps of providing a first layer of metal foil provided with an embossedtexture whereby the foil is provided with an array of miniatureembossing on at least a part of the foil; providing a second layer ofthermoplastic flouropolymer; providing a third layer of fabric;assembling the first, second and third layers, pressing the assembly oflayers while heating the assembly in a heating zone to a temperatureabove the melting point of the intermediate second web for apredetermined amount of time for laminating the first and third webstogether; and cooling the laminate while pressing the laminate in acooling zone.
 12. A method of manufacturing a laminate including thesteps of providing a first layer of metal foil; providing a second layerof thermoplastic flouropolymer; providing a third layer of fabric;assembling the first, second and third layers, pressing the assembly oflayers while heating the assembly in a heating zone to a temperatureabove the melting point of the intermediate second web for apredetermined amount of time for laminating the first and third webstogether, whereby the metal foil of the first layer is provided with anenchased texture during the pressing action, and cooling the laminatewhile pressing the laminate in a cooling zone.
 13. A method according toclaim 12, whereby the metal foil of the first layer is provided with anenchased texture during the pressing in the heating zone.
 14. A methodaccording to claim 12 or 13, whereby the supporting fabric is providedwith pre-formed arrays of embossing for providing the metal foil with anenchased texture during the pressing action.
 15. A method according toany of claims 12 to 14, whereby the metal foil is provided with anenchased texture corresponding to the surface texture of the wovenfabric of the third layer during the pressing.
 16. A method according toclaim 15, whereby the metal foil is pre-embossed and is also providedwith an encased texture corresponding to the surface texture of thewoven fabric of the third layer during the pressing.
 17. A methodaccording to any of the claims 11 to 16, whereby the pressing isperformed by pressing members pressed against each other from each sideof the assembly of layers for a predetermined time period, and saidmembers are heated to a temperature of at least 380° C., preferablywithin the range of 327° C. and 400° C.
 18. A method according to any ofthe claims 11 to 17, whereby a supporting fabric is provided on eachside of the assembled web to protect the layers in the heating zone. 19.A method according to any of claims 11 to 18, whereby the pressing timeis between 10 and 300 seconds, and the pressure is within the range of10N/cm² and 1000N/cm² depending on metal foil used.
 20. A methodaccording to any of claims 11 to 19, whereby the cooling is performed bycooling members that are pressed against the laminate and providing withcooling means for cooling the laminate to a temperature between 0° C. to250° C., preferably approx. 20-30° C.
 21. A method according to any ofclaims 11 to 20, whereby a supporting fabric is provided on each side ofthe assembled layer to protect the webs in the cooling zone.